Blast Media Size: How Shot Size Affects Impact Energy and Surface Finish

Aside from choosing the type of blast media, selecting the most effective blast media size is extremely important for your shot blasting operation. When selecting a size for a particular job, conventional wisdom says to use the smallest size shot that will get the job done. Frequently, this entails removal of heavy flash or thick paint from your parts. The goal is to select the shot that will have the energy to remove these items in a timely manner while imparting a uniform finish on the parts.

Impact Energy

The impact energy of a single piece of shot can be defined by the equation:

E = 1/2 MV2

M = the mass of the shot piece

V = the velocity or wheel speed at which the shot is being propelled

When you double the size of the shot used in your shot blasting process, you increase the impact energy of each piece of shot by 8 times. Shot is 3 dimensional, so doubling the size increases the mass by the cube of the shot diameter. Small changes up or down in shot size can have a dramatic influence on flash removal efficiency or warping of a part.

Uniformity of Surface Finish

Changes in the size of shot used also will have a large effect on the uniformity of surface finish on the part. A larger shot will require longer blast cycle times to saturate the surface of your blasted part.

One Lb of RSZ-850-ZA4 (S-280 equivalent) has 172,000 pieces

One Lb of RSZ-500-ZA4 (S-170 equivalent) has 454,000 pieces

As an example, a 15 HP blast wheel throws around 375 lb of zinc abrasive per minute, so:

In one minute using RSZ-850-ZA4 the blast wheel will throw 65,625,000 pieces of shot

In one minute using RSZ-500-ZA4 the blast wheel will throw 170,250,000 pieces of shot

Download the Case Study to learn how a company improved blast cycle times by 300%

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